In recent years, in the fields of semiconductor, optical magnetic recording, etc., as demands for higher density, higher integration and others have increased, techniques have become essential for fine pattern processing of about several hundreds to tens of nanometers or less. Therefore, to achieve the fine pattern processing, elemental techniques of each process have been studied actively such as a mask•stepper, exposure, dry etching and resist material.
For example, in the process of mask•stepper are studied techniques for using a particular mask called the phase shift mask to provide light with a phase difference, and enhancing fine pattern processing accuracy by the effect of interference, liquid dip techniques for filling between a lens for a stepper and a wafer with liquid, largely refracting light passed through the lens, and thereby enabling fine pattern processing, etc. However, the former techniques require huge costs for mask development, the latter techniques require an expensive apparatus, and it is thus extremely difficult to reduce manufacturing costs.
On the other hand, many studies have proceeded also on resist materials, and currently, the most common resist material is a photoreactive organic resist (hereinafter, also referred to as a photoresist) that reacts by an exposure light source such as ultraviolet light, electron beam and X-rays (for example, see Patent Document 1 and Non-patent Document 1).
FIG. 1 is a graph illustrating the relationship between a spot diameter of laser light and laser intensity. In FIG. 1, the horizontal axis represents the spot diameter (Rs) of laser light, and the vertical axis represents laser light intensity (E). In the laser light used in exposure, the intensity (E) of the laser light focused by the lens generally shows the Gaussian distribution with respect to the spot diameter (Rs) as shown in FIG. 1. At this point, the spot diameter (Rs) is defined by 1/e2. In general, in the reaction of a photoresist, the photoreaction starts by absorbing energy represented by E=hν (E: energy, h: Planck constant, ν: wavelength). Accordingly, the photoreaction is not dependent on the intensity of the light strongly, and is rather dependent on the wavelength of the light, and therefore, the photoreaction occurs in the entire area (hereafter, referred to as “exposed area”) irradiated with the light. Therefore, when the photoresist is used, the area corresponding to the spot diameter (Rs) is the exposed area.
The method of using a photoresist is an extremely effective method in forming fine patterns of about hundreds of nanometers, and the photoreaction proceeds in the area corresponding to the spot diameter. Therefore, to form a finer pattern, it is necessary to expose with a smaller spot diameter than the pattern required in principle. Accordingly, it is indispensable to use a KrF laser, ArF laser or the like with short wavelengths as an exposure light source. However, these light source apparatuses are remarkably large-size and expensive, and are unsuitable from the viewpoint of reducing manufacturing costs. Further, in the case of using the exposure light source of electron beam, X-rays or the like, since it is necessary to evacuate the exposure atmosphere to a vacuum state, using a vacuum chamber is required, and there are significant limitations from the viewpoints of the cost and increases in the size.
On the other hand, when a substance is irradiated with the laser light showing the Gaussian distribution as shown in FIG. 1, the temperature of the substance also shows the same Gaussian distribution as the intensity distribution of the laser light. FIG. 2 is a graph illustrating the relationship between an exposed area of the laser light and temperature. In FIG. 2, the horizontal axis represents the exposed area (Ae), and the vertical axis represents the temperature (T). In this case, when a resist (hereinafter, referred to as “heat-reactive resist”) that reacts at a predetermined temperature or more is used, as shown in FIG. 2, since the reaction proceeds only in the portion becoming the predetermined temperature (resist reaction temperature: Tr) or more, it is made possible to expose the area (Ae) smaller than the spot diameter (Rs). In other words, without shortening the wavelength of the exposure light source, it is possible to form the pattern finer than the spot diameter (Rs), and by using the heat-reactive resist, it is possible to reduce the effect of the wavelength of the exposure light source.
In the field of optical recording, proposed are techniques for using WOx, MoOx, chalcogenide glass (Ag—As—S system) or the like as the heat-reactive resist, and forming a fine pattern by exposing with a semiconductor laser or 476-nm laser (see Patent Document 2 and Non-patent Document 2). The optical disks used in the optical recording field are a general name for media such that laser is applied to the disk coated with the resist material to read information recorded on fine concavities and convexities provided on the disk surface. In the optical disk, as the interval of a recording unit called the track pitch is narrower, the recording density increases, and the data capacity recordable for each area increases. Therefore, in order to increase the recording density, researches are performed on fine concavo-convex pattern processing techniques using resist materials.
However, the researches using the heat-reactive resist materials respond to requirements for narrowing (increasing the recording density of information) the pitch of the pattern in the film surface direction, and there has been no requirement for forming a deep groove in the film thickness direction. On the other hand, in recent years, in many fields, there have been increasing requirements for application using a pattern shape having a deep groove in the film thickness direction. As the depth of the groove in the film thickness direction, the thickness of the film of the heat-reactive resist is the depth of the groove in the film thickness direction without modification, and to form a groove deeply, it is necessary to thicken the heat-reactive resist. However, in the heat-reactive resist, by thickening the film thickness, uniformity of the thermal reaction by exposure is lost in the film thickness direction. As a result, there are problems that it is difficult to form a deep groove in the film thickness direction, and that processing accuracy of a fine pattern also degrades in the film surface diction.
Then, such a method is also conceivable that a film (hereinafter, referred to as “etching layer”) with a thickness corresponding to a desired groove depth is beforehand formed under the heat-reactive resist. In this case, the heat-reactive resist provided with a pattern shape by exposure•development is used as a mask. Then, by etching the etching layer using the mask, a deep groove is formed. Generally, dry etching is used to etch uniformly in the film thickness direction. For example, when SiO2 is used in the etching layer, it is possible to perform dry etching using a fluorine-containing gas. In the case of processing by dry etching, the heat-reactive resist used as a mask is required to have resistance to dry etching using a fluorine-containing gas as well as permitting the fine pattern processing.
On the other hand, also in dry etching techniques, since a wide variety of etching shapes is required corresponding to applications, many studies are implemented such as a study for improving an electrode structure and the like of a dry etching apparatus and a study for controlling gas species for etching to use. For example, as techniques for deepening a groove depth of a pattern, there is the Bosch method developed by Bosch Corporation. In the Bosch method is reported the technique for switching the atmosphere inside a process chamber between an etching gas (for example, CF4 gas and SF6 gas) and a side wall protection gas (for example, gas with F/C of 3 or less such as C4F8 gas) and thereby forming a deep groove in the film thickness direction using photoresists (see Non-patent Document 3). Further, in dry etching using the side wall protection gas, a protective film of fluorocarbon is formed on the side wall of the etching layer formed by dry etching. The technique is further reported together with the photoresists in which by using this protective film, the dry etching rate in the film thickness direction and the dry etching rate in the film surface direction are changed to attain a desired etching angle (taper angle).
Previously, with respect to dry etching resistance of inorganic-based heat-reactive resist materials, the inventor of the present invention found out that elements such that the boiling point of the fluoride is 200° C. or more has high dry etching resistance (see Patent Document 3).